Method for producing busbar, busbar, and battery module

ABSTRACT

A method for producing busbar includes a step of applying pressure to pressure-weld a plurality of electric wires in a plurality of first regions in a bundle of the plurality of electric wires, the first regions being arranged at a predetermined interval in the extending direction of the bundle, to form a plurality of terminal joints that are joined to the output terminals of the respective batteries.

TECHNICAL FIELD

The present invention relates to a method for producing a busbar, abusbar, and a battery module.

BACKGROUND ART

As a power source requiring a high output voltage, such as a powersource for a vehicle, a battery module in which a plurality of batteriesare electrically connected is known. Conventionally, in such a batterymodule, output terminals of adjacent batteries have been connected toeach other by busbars. With respect to the busbar used for the batterymodule, PTL 1 discloses a technique of providing a bend in the middle ofa plate-shaped busbar to absorb relative displacement between outputterminals connected by the busbar.

CITATION LIST Patent Literature

PTL 1: Unexamined Japanese Patent Publication No. 6-140020

SUMMARY OF THE INVENTION Technical Problem

In recent years, a further increase in the capacity of the batterymodule has been demanded, and for satisfying this demand, the capacityof the battery has been increased. As the capacity of the batteryincreases, the amount of dimensional change in the battery increases, sothat the amount of relative displacement between the output terminalsconnected by the busbar increases. Therefore, the busbar is required tofollow the larger displacement of the output terminals to increase thestability of the electrical connection between the batteries.

The present invention has been made in view of these circumstances, andan object of the present invention is to provide a technique forenhancing the stability of electrical connection between batteries.

Solution to Problem

One aspect of the present invention is a production method for a busbar.The production method is a method for producing a busbar thatelectrically connects a plurality of batteries, the method including astep of applying pressure to pressure-weld a plurality of electric wiresin a plurality of first regions in a bundle of the plurality of electricwires, the first regions being arranged at a predetermined interval inan extending direction of the bundle, to form a plurality of terminaljoints that are joined to output terminals of the respective batteries.

Another aspect of the present invention is a busbar. The busbar is abusbar electrically connecting a plurality of batteries, the busbarincluding: a plurality of terminal joints that are joined to outputterminals of the respective batteries; and a coupler that connects theplurality of terminal joints. The coupler is formed of anon-pressure-welded part in a bundle of a plurality of electric wires,and each of the plurality of terminal joints is formed of apressure-welded part in the bundle of the plurality of electric wires.

Another aspect of the present invention is a battery module. The batterymodule includes the busbar of the above aspect and a plurality ofbatteries electrically connected by the busbar.

Note that any combination of the above components and the expression ofthe present invention converted between methods, devices, systems, andthe like are also effective as aspects of the present invention.

Advantageous Effect of Invention

According to the present invention, it is possible to enhance thestability of the electrical connection between the batteries.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a battery module according to anexemplary embodiment.

FIG. 2(A) is a perspective view of a busbar. FIG. 2(B) is a side view ofthe busbar.

FIG. 3(A) to FIG. 3(D) are side views illustrating a production processfor the busbar.

FIG. 4(A) to FIG. 4(E) are side views illustrating a production processfor a busbar according to Modification 1.

FIG. 5 is a perspective view of a busbar according to Modification 2.

DESCRIPTION OF EMBODIMENT

Hereinafter, the present invention will be described based on apreferred exemplary embodiment with reference to the drawings. Theexemplary embodiment does not limit the invention but is illustrative,and not all features and combinations thereof described in the exemplaryembodiment are necessarily essential to the invention. The same orequivalent components, members, and processes illustrated in thedrawings are denoted by the same reference numerals, and redundantdescriptions are omitted as appropriate. Further, the scales and shapesof the respective parts illustrated in the drawings are set forconvenience in order to facilitate the description and are not to beinterpreted in a limited manner unless otherwise mentioned. Further,when terms such as “first” and “second” are used in the presentspecification or claims, the terms are not intended to indicate anyorder or importance but to distinguish one configuration from another,unless otherwise mentioned. In the drawings, illustration is made,omitting some of the members which are not important for explaining theexemplary embodiment.

FIG. 1 is a perspective view of a battery module according to theexemplary embodiment of the present invention. Battery module 1 mainlyincludes a plurality of batteries 2, a plurality of busbars 4, a pair ofend-plates 6, and a pair of restraint members 8.

Each battery 2 is, for example, a rechargeable secondary battery such asa lithium-ion battery, a nickel-hydrogen battery, or a nickel-cadmiumbattery. Battery 2 is a so-called square battery and has a flatrectangular parallelopiped outer can. An opening (not illustrated)having a substantially rectangular shape is provided on one surface ofthe outer can, and an electrode body, an electrolyte, and the like arehoused in the outer can via the opening. Sealing plate 10 for sealingthe outer can is provided in the opening of the outer can. Sealing plate10 is a rectangular plate.

Sealing plate 10 is provided with positive output terminal 12 near oneend in the longitudinal direction and negative output terminal 12 nearthe other end. The pair of output terminals 12 are electricallyconnected to a positive electrode plate and a negative electrode plateconstituting the electrode body. Hereinafter, as appropriate, positiveoutput terminal 12 will be referred to as positive terminal 12 a, andnegative output terminal 12 will be referred to as negative terminal 12b. When it is not necessary to distinguish the polarity of outputterminal 12, positive terminal 12 a and negative terminal 12 b arecollectively referred to as output terminal 12. The outer can, sealingplate 10, and output terminal 12 are conductive materials, such asmetal. Sealing plate 10 and the opening of the outer can are joined bywelding or the like. Each output terminal 12 is inserted through athrough hole (not illustrated) formed in sealing plate 10. An insulatingseal member is interposed between each output terminal 12 and eachthrough hole.

In the present exemplary embodiment, for convenience of description, thesurface on the side where sealing plate 10 is disposed is a top surfaceof battery 2, and the surface on the side opposite to sealing plate 10is a bottom surface of battery 2. Battery 2 has two main surfacesconnecting the top surface and the bottom surface. The main surface hasthe largest area among the six surfaces of battery 2. The main surfaceis a long side surface connected to the long sides of the top surfaceand the bottom surface. The remaining two surfaces, except for the topsurface, the bottom surface, and the two main surfaces, are the sidesurfaces of battery 2. The side surface is a short side surfaceconnected to the short sides of the top surface and the bottom surface.These directions and positions are specified for convenience. Thus, forexample, it is not meant that a portion defined as the top surface inthe present invention is always located above a part defined as thebottom surface.

Sealing plate 10 is provided with a safety valve (not illustrated)between the pair of output terminals 12. The safety valve is configuredto open when the internal pressure of the outer can rises to apredetermined value or more and to release the internal gas. The safetyvalve of each battery 2 is connected to a gas duct (not illustrated),and the gas inside the battery is discharged from the safety valve tothe gas duct.

The plurality of batteries 2 are laminated at predetermined intervalswith the main surfaces of adjacent batteries 2 facing each other. Notethat “lamination” means arranging a plurality of members in any onedirection. Thus, the lamination of batteries 2 includes horizontallyarranging the plurality of batteries 2. Batteries 2 are arranged suchthat output terminal 12 face the same direction. In the presentexemplary embodiment, for convenience, each battery 2 is disposed suchthat output terminal 12 faces vertically upward. Two adjacent batteries2 are laminated such that positive terminal 12 a of one battery 2 andnegative terminal 12 b of another battery 2 are adjacent to each other.

Positive terminal 12 a and negative terminal 12 b are electricallyconnected by busbar 4. That is, busbar 4 electrically connects theplurality of batteries 2. Output terminal 12, located on the outermostside of the series connection, is electrically connected to an externalconnection terminal (not illustrated). The external connection terminalis connected to an external load via wiring led to the outside ofbattery module 1. Note that output terminals 12 of the plurality ofadjacent batteries 2 of the same polarity may be connected in parallelby busbar 4 to form a battery block, and the battery blocks may beconnected to each other, or the battery blocks and battery 2 may beconnected in series. The structure of busbar 4 will be described laterin detail.

Battery module 1 has a plurality of separators (not illustrated). Eachseparator is also called an insulating spacer and is disposed betweentwo adjacent batteries 2 to electrically insulate the outer cans of twoadjacent batteries 2 from each other. Further, the separator is disposedbetween battery 2 and end-plate 6 to electrically insulate the outer canof battery 2 from end-plate 6. Each separator is made of, for example,an insulating resin. Examples of the resin constituting the separatorinclude thermoplastic resins such as polypropylene (PP), polybutyleneterephthalate (PBT), polycarbonate (PC), and Noryl (registeredtrademark) resin (modified PPE).

The plurality of laminated batteries 2 and the plurality of separatorsare sandwiched by the pair of end-plates 6. Each end-plate 6 is made of,for example, a metal plate. The pair of end-plates 6 are arranged so asto be adjacent to batteries 2 at both ends in laminating direction X ofbatteries 2 via the separators. The surface of end-plate 6 facing themain surface of battery 2 is provided with a screw hole (notillustrated) into which a screw (not illustrated) is screwed.

The pair of restraint members 8 are also called bind bars and areelongated members with longitudinal directions being laminatingdirection X. The pair of restraint members 8 are arranged to face eachother in direction Y orthogonal to laminating direction X and parallelto the longitudinal direction of sealing plate 10. The plurality ofbatteries 2, the plurality of separators, and the pair of end-plates 6are interposed between the pair of restraint members 8. Each restraintmember 8 has rectangular flat part 8 a extending in parallel with theside surface of battery 2, and four eaves 8 b projecting from therespective end side of flat part 8 a toward battery 2.

Flat part 8 a is provided with opening 8 c for exposing the side surfaceof battery 2. Opening 8 c is preferably arranged so as not to affect therigidity of restraint member 8 against the external force in laminatingdirection X as much as possible. This can reduce the weight of restraintmember 8 while maintaining the rigidity of restraint member 8. Two eaves8 b facing each other in laminating direction X are provided withthrough holes 8 d through which screws are inserted.

Battery module 1 is assembled as follows, for example. That is, first, aplurality of batteries 2 and a plurality of separators are alternatelylaminated, and these are sandwiched between the pair of end-plates 6 inlaminating direction X to form an assembly. The assembly is sandwichedin direction Y by the pair of restraint members 8. Each restraint member8 is aligned such that through hole 8 d overlaps the screw hole ofend-plate 6. The screw is inserted into through hole 8 d and screwedinto the screw hole. Thus, the plurality of batteries 2 and theplurality of separators are restrained by engaging the pair of restraintmembers 8 with the pair of end-plates 6.

The plurality of batteries 2 are positioned in laminating direction X bybeing clamped in laminating direction X by restraint members 8. Further,the plurality of batteries 2 have bottom surfaces in contact with eaves8 b on the lower side of restraint member 8 via the separators, and havethe top surfaces in contact with eaves 8 b on the upper side ofrestraint member 8 via the separators, so that the batteries 2 arepositioned in direction Z in which the top surfaces and the bottomsurfaces are arranged. After the completion of the positioning, busbar 4is attached to output terminal 12 of each battery 2, and each outputterminal 12 is connected electrically. Subsequently, a cover member (notillustrated) is attached so as to cover the top surface of each battery2 to obtain battery module 1.

Next, busbar 4 according to the present exemplary embodiment will bedescribed in detail. FIG. 2(A) is a perspective view of the busbar. FIG.2(B) is a side view of the busbar. Busbar 4 includes a plurality ofterminal joints 14 and coupler 16. Respective terminal joints 14 arejoined to output terminals 12 of respective batteries 2. In the presentexemplary embodiment, two batteries 2 are connected in series by busbar4. Therefore, busbar 4 has two terminal joints 14.

Coupler 16 connects the plurality of terminal joints 14. Coupler 16 isformed of a non-pressure-welded part in a plurality of electric wires,that is, a bundle of conductive wires. Hence the electric wires are notconnected to each other in coupler 16. In the present exemplaryembodiment, the bundle of electric wires constituting coupler 16 is aflat stranded wire in which a plurality of electric wires are stranded.Examples of the material of the electric wire include copper andaluminum. When the electric wire is a copper wire, nickel plating or tinplating may be applied. Coupler 16 of the present exemplary embodimentis curved so as to protrude in a direction away from battery 2.

Two terminal joints 14 are arranged at both ends of busbar 4 inlaminating direction X of battery 2. Coupler 16 is disposed between twoterminal joints 14 in laminating direction X. Busbar 4 of the presentexemplary embodiment includes voltage detection line connector 18.Voltage detection line connector 18 is disposed between each terminaljoint 14 and coupler 16. Therefore, busbar 4 has a structure in whichterminal joint 14, voltage detection line connector 18, coupler 16,voltage detection line connector 18, and terminal joint 14 are arrangedin this order in laminating direction X. A voltage detection line (notillustrated) for detecting the voltage of each battery 2 is electricallyconnected to either one of voltage detection line connectors 18 bywelding or the like.

Each terminal joint 14 and each voltage detection line connector 18 areformed of a pressure-welded part in the bundle of the plurality ofelectric wires. That is, in the bundle of the plurality of electricwires, the pressure-welded region constitutes terminal joint 14 andvoltage detection line connector 18, and the non-pressure-welded regionconstitutes coupler 16. Therefore, busbar 4 is an integrally formedmetal product and does not have a structure for mutually fixing eachpart of terminal joint 14, coupler 16, and voltage detection lineconnector 18, such as a weld, caulking fixing part, or the like.

Each terminal joint 14 has fitting part 20 of output terminal 12.Fitting part 20 of the present exemplary embodiment is formed of a notchprovided at the end of terminal joint 14. With output terminal 12 fittedto fitting part 20, terminal joint 14 is joined to output terminal 12 bywelding or the like. Thus, each output terminal 12 is electricallyconnected via busbar 4.

Each terminal joint 14 has a flat plate shape with its surface beingsmooth so as not to interfere with the electrical connection with outputterminal 12. Similarly, each voltage detection line connector 18 has aflat plate shape with its surface being smooth so as not to interferewith the electrical connection with the voltage detection line. Thethickness of each voltage detection line connector 18 is larger than thethickness of each terminal joint 14. It is thereby possible to shortenthe welding time by thinning terminal joint 14, and to prevent anincrease in the electric resistance of busbar 4 by thickening voltagedetection line connector 18. It is also possible to increase the heatcapacity of busbar 4 by increasing the thickness of voltage detectionline connector 18.

Each terminal joint 14 has slope 22 at an edge close to coupler 16, thatis, an edge in contact with voltage detection line connector 18. Slope22 has a thickness gradually increasing toward coupler 16. By providingslope 22, it is possible to enhance the coupling strength betweenterminal joint 14 and the side of coupler 16 (voltage detection lineconnector 18) can be enhanced. In other words, when busbar 4 isdeformed, it is possible to prevent the stress from being concentratedon the coupler between terminal joint 14 and voltage detection lineconnector 18.

Coupler 16 formed of the non-pressure-welded part in the bundle of theplurality of electric wires can be deformed following this displacementwhen two output terminals 12 connected by busbar 4 are relativelydisplaced. Therefore, busbar 4 with coupler 16 has high flexibility ascompared to a conventional busbar formed entirely of plate material.

Coupler 16 can follow the displacement of output terminal 12 in adirection intersecting with laminating direction X, that is, thedirection of the YZ plane, by the deformation of coupler 16 itself.Coupler 16 has a curved shape protruding in direction Z. Hence coupler16 can also follow the displacement of output terminal 12 in laminatingdirection X. Further, since coupler 16 of the present exemplaryembodiment is formed of the flat stranded wire, the expansion andcontraction of coupler 16 can follow the displacement of output terminal12 in laminating direction X. When coupler 16 is formed of the flatstranded wire, coupler 16 may not have a curved shape.

Next, a method for producing busbar 4 according to the present exemplaryembodiment will be described in detail. FIG. 3(A) to FIG. 3(D) are sideviews illustrating a production process for the busbar. First, asillustrated in FIG. 3(A), for example, flat stranded wire 24 is preparedas a bundle of a plurality of electric wires. Flat stranded wire 24 hasan elongated shape being long on one side. Then, as illustrated in FIG.3(B), the center part of flat stranded wire 24 is bent to form curve 26.

Subsequently, as illustrated in FIG. 3(C), a step of forming precursorterminal joint 28 and voltage detection line connector 18 is performed.In this step, a predetermined region of flat stranded wire 24 ispressure-welded using a press device or the like to form precursorterminal joint 28 and voltage detection line connector 18. Specifically,in flat stranded wire 24, first press die 34 is pressed against aplurality of second regions 32 to apply predetermined pressure on eachsecond region 32. In this step, the magnitude of the force applied tosecond region 32 is, for example, 1000 kN to 4000 kN. If necessary,second region 32 may be heated at the time when second region 32 ispressed by first press die 34.

Each second region 32 is a region including first region 30. Firstregion 30 is a region where terminal joint 14 is finally formed, andfirst regions 30 are arranged at a predetermined interval in theextending direction of the bundle of the plurality of electric wires. Inthe present exemplary embodiment, two first regions 30 are located atboth ends of the flat stranded wire 24. Accordingly, two second regions32 are arranged with curve 26 interposed therebetween.

By first press die 34 being pressed against each second region 32, aplurality of electric wires are pressure-welded in each second region32. As a result, precursor terminal joint 28 is formed in first region30, and voltage detection line connector 18 is formed in remainingregion 36 of second region 32 except for first region 30. Curve 26located between two second regions 32 remains in the state of flatstranded wire 24 without being pressure-welded.

Subsequently, as illustrated in FIG. 3(D), a step of forming terminaljoint 14 is performed. In this step, the plurality of first regions 30are further pressure-welded using a press device or the like to formterminal joint 14. Specifically, second press die 38 is pressed againsteach first region 30 to apply predetermined pressure on each firstregion 30. In this step, the magnitude of the force applied to firstregion 30 is, for example, 1000 kN to 4000 kN. If necessary, firstregion 30 may be heated at the time when first region 30 is pressed bysecond press die 38.

By second press die 38 being pressed against first region 30, aplurality of electric wires, in other words, precursor terminal joint 28is further pressure-welded in each first region 30. As a result, thethickness of precursor terminal joint 28 of each of first regions 30 isreduced to form a terminal joint 14.

Second press die 38 has tapered part 38 b at the edge ofpressure-welding surface 38 a that comes into contact with flat strandedwire 24. Tapered part 38 b is disposed at the edge of pressure-weldingsurface 38 a, which is close to the non-pressure-welded region (curve 26and remaining region 36) not pressure-contacted by second press die 38.Tapered part 38 b is inclined from the center of pressure-weldingsurface 38 a toward the outside so as to be separated from first region30.

First region 30 is pressure-welded by second press die 38 having such ashape, thereby forming slope 22 at the edge close to thenon-pressure-welded region in first region 30. Slope 22 has thethickness gradually increasing toward the non-pressure-welded region.Therefore, the step of forming terminal joint 14 includes the step offorming slope 22.

Curve 26 is not pressure-welded by either first press die 34 or secondpress die 38, and the plurality of electric wires remain in anon-pressure-welded state. This portion serves as coupler 16. Byproviding second press die 38 with a shape corresponding to fitting part20, fitting part 20 can be formed simultaneously with the formation ofterminal joint 14. By the above steps, busbar 4 is obtained.

As described above, the method for producing busbar 4 according to thepresent exemplary embodiment includes a step of applying pressure topressure-weld a plurality of electric wires in a plurality of firstregions 30 in a bundle of the plurality of electric wires, the pluralityof first regions 30 being arranged at a predetermined interval in theextending direction of the bundle, to form a plurality of terminaljoints 14 that are joined to output terminals 12 of respective batteries2. That is, in the production method of busbar 4 according to thepresent exemplary embodiment, busbar 4 is produced by pressure-weldingthe bundle of the plurality of electric wires to form terminal joint 14and using the non-pressure-welded part as coupler 16.

Accordingly, busbar 4 of the present exemplary embodiment obtained bysuch a production method includes: coupler 16 that connects theplurality of terminal joints 14 and is formed of the non-pressure-weldedpart in the bundle of plurality of electric wires; and the plurality ofterminal joint 14 that is joined to output terminals 12 of respectivebatteries 2 and is formed of the pressure-welded part in the bundle ofthe plurality of electric wires. Battery module 1 of the presentexemplary embodiment includes busbar 4 and a plurality of batteries 2electrically connected by busbar 4.

Coupler 16 is formed of the bundle of the electric wires not joined toeach other and hence has higher flexibility than a plate material.Busbar 4 absorbs the displacement of output terminal 12 by thedeformation of coupler 16. Therefore, busbar 4 of the present exemplaryembodiment can follow larger displacement of output terminal 12 ascompared to the conventional busbar in which the bend is provided in theintermediate region of the plate material. Further, it is possible tofollow the displacement of output terminal 12 in more directions. It isthereby possible to further prevent a load from being applied to thejoint between terminal joint 14 and output terminal 12 due to thedisplacement between output terminals 12. As a result, it is possible toenhance the reliability and the stability of the connection betweenoutput terminals 12.

Further, in the conventional busbar in which the flexibility is ensuredin the bend, in order to cope with an increase in the amount ofdisplacement of output terminal 12 accompanying an increase in thecapacity of battery 2, it has been necessary to increase the size of thebend. In this case, the size of the busbar in direction Z is increased,that is, the height of the busbar is increased. In contrast, busbar 4 ofthe present exemplary embodiment absorbs the displacement of outputterminal 12 by coupler 16 formed of electric wires. Furthermore, coupler16 of the present exemplary embodiment is flat stranded wire 24, andcoupler 16 itself expands and contracts. It is thus possible to copewith an increase in the amount of displacement of output terminal 12while preventing an increase in the height of busbar 4.

In addition, a conventional wiring cord, in which caulking terminals(also known as crimp terminals) are provided at both ends of an electricwire, and the two caulking terminals and the electric wire are arrangedon a straight line, is difficult to install because the interval betweentwo output terminals 12 is narrow. That is, the caulking terminal has afixing part fixed to the electric wire in addition to a joint with theoutput terminal. Therefore, in the structure in which the two caulkingterminals and the electric wire are arranged on a straight line, eventhe total dimension of the two caulking terminals in laminatingdirection X alone can exceed the interval between two output terminals12. In this case, it is difficult to install a busbar having thisstructure unless the distance between adjacent batteries 2 is increased.

However, increasing the distance between batteries 2 leads to anincrease in the size of battery module 1 or a decrease in the energydensity, which runs counter to the demand for an increase in thecapacity of batteries 2 and thus battery module 1. In contrast, inbusbar 4 of the present exemplary embodiment, the non-pressure-weldedpart in the bundle of the plurality of electric wires constitutescoupler 16, and the pressure-welded part in the bundle constitutesterminal joint 14. That is, busbar 4 is an integrally formed metalproduct, and terminal joint 14 is continuous with coupler 16 withouthaving a fixing part fixed to coupler 16. This enables an electricalcontact between adjacent output terminals 12 connected to each otherwithout increasing the distance between batteries 2. Further, a moreextension region of coupler 16 in laminating direction X can be ensured.It is thereby possible to further enhance the followability of coupler16 to the displacement of two output terminals 12.

As described above, according to busbar 4 obtained by the productionmethod of the present exemplary embodiment, even when the amount ofdimensional change in battery 2 increases as the capacity of battery 2increases, stable electrical connection between batteries 2 can bemaintained. That is, the stability of the electrical connection betweenbatteries 2 can be enhanced. Thus, the reliability of battery module 1can be enhanced. It is also possible to avoid an increase in the size ofbattery module 1 or a decrease in the energy density caused by anincrease in the height of busbar 4 or an increase in the intervalbetween batteries 2.

In the method for producing busbar 4 according to the present exemplaryembodiment, the step of forming terminal joints 14 includes formingslope 22 at the edge close to the non-pressure-welded region in thefirst region 30. Slope 22 has a thickness gradually increasing towardthe non-pressure-welded region. Accordingly, busbar 4 according to thepresent exemplary embodiment has, at the edge close to coupler 16 interminal joint 14, slope 22 with its thickness gradually increasingtoward coupler 16. By changing the thickness of the edge of terminaljoint 14 stepwise or continuously as thus described, when the force isapplied to busbar 4 from the outside, stress concentration on the edgeof terminal joint 14 can be reduced. Therefore, it is possible tofurther enhance the stability of the electrical connection betweenbatteries 2.

The method for producing busbar 4 according to the present exemplaryembodiment includes a step that is performed before the step of formingterminal joints 14, the method including the step of applying pressureto pressure-weld a plurality of electric wires in a plurality of secondregions 32 including respective first regions 30 in the bundle to formprecursor terminal joint 28 in first region 30, and forming voltagedetection line connector 18 in remaining region 36 of second region 32except for first region 30. Therefore, busbar 4 according to the presentexemplary embodiment includes voltage detection line connector 18disposed between terminal joint 14 and coupler 16.

By providing voltage detection line connector 18 in busbar 4, theelectrical connection between busbar 4 and the voltage detection linecan be obtained more reliably. Thus, the reliability of battery module 1can be further enhanced. By first-stage pressure-welding, voltagedetection line connector 18 and precursor terminal joint 28 are formed,and by second-stage pressure-welding, precursor terminal joint 28 isfinished into terminal joint 14. This can make the thickness of voltagedetection line connector 18 larger than the thickness of terminal joint14. Therefore, it is possible to reduce the welding time by thinningterminal joint 14, thus preventing battery 2 from being damaged by heatduring welding, and to prevent an increase in the electric resistance ofbusbar 4 and a decrease in the heat capacity by thickening voltagedetection line connector 18.

The exemplary embodiment of the present invention has been described indetail. The exemplary embodiment described above is only a specificexample for carrying out the present invention. The content of theexemplary embodiment does not limit the technical scope of the presentinvention, and many design changes such as changes, additions, anddeletions of components are possible without departing from the spiritof the invention defined in the claims. The new modified exemplaryembodiment has both the effects of the combined exemplary embodiment andthe modification. In the exemplary embodiment described above, adescription such as “of the present exemplary embodiment” or “in thepresent exemplary embodiment” is attached to emphasize the content onwhich the design change as thus described can be made, but the designchange is allowed even in content without such a description. Anycombination of components included in the exemplary embodiment is alsoeffective as an aspect of the present invention. The hatching on thecross-section of the drawing does not limit the material of the objectto which the hatching has been applied.

(Modification 1)

FIG. 4(A) to FIG. 4(E) are side views illustrating a production processfor a busbar according to Modification 1. The present modification isdifferent from the exemplary embodiment in including a heat-weldingstep. Specifically, as illustrated in FIG. 4(A), for example, flatstranded wire 24 is prepared as a bundle of a plurality of electricwires. Then, as illustrated in FIG. 4(B), the center part of flatstranded wire 24 is bent to form curve 26.

Subsequently, as illustrated in FIG. 4(C), the heat-welding step isperformed. In this step, hot plate 40 is pressed against the pluralityof second regions 32 to heat and pressurize each second region 32. As aresult, a plurality of electric wires extending in the respective secondregions 32 are heat-welded to each other to form heat-welded part 42. Inthis step, the heating temperature of second region 32 is, for example,300° C. to 1200° C. The magnitude of the force applied to second region32 is, for example, 1000 kN to 4000 kN.

Subsequently, as illustrated in FIG. 4(D), a step of forming precursorterminal joint 28 and voltage detection line connector 18 is performed.In this step, first press die 34 is pressed against the plurality ofsecond regions 32 to apply predetermined pressure on each second region32. By first press die 34 being pressed against each second region 32, aportion of heat-welded part 42 extending in first region 30 becomesprecursor terminal joint 28, and a portion of second region 32 extendingin remaining region 36 becomes voltage detection line connector 18.

Subsequently, as illustrated in FIG. 4(e), a step of forming terminaljoint 14 is performed. In this step, second press die 38 is pressedagainst each first region 30 to apply predetermined pressure on eachfirst region 30. By second press die 38 being pressed against firstregion 30, precursor terminal joint 28 becomes a terminal joining part14. Further, by second press die 38 being pressed against first region30, slope 22 is formed at the edge close to the non-pressure-weldedregion in first region 30.

Curve 26 is not heated or pressure-welded by any of hot plate 40, firstpress die 34, and second press die 38, and a plurality of electric wiresremain in a non-pressure-welded state. This portion serves as coupler16. By the above steps, busbar 4 is obtained.

In the present modification, the region of flat stranded wire 24 to besubjected to press working is subjected to heat-welding treatment beforepress working. This facilitates subsequent press working. Further, theworking accuracy of terminal joint 14 and voltage detection lineconnector 18 in press working can be enhanced. Note that the pressworking using first press die 34 may be omitted, and voltage detectionline connector 18 and precursor terminal joint 28 may be formed byheat-welding.

(Modification 2)

FIG. 5 is a perspective view of a busbar according to Modification 2. Inthe exemplary embodiment, busbar 4 has two terminal joints 14, but thepresent invention is not limited to this configuration, and busbar 4 mayhave three or more terminal joints 14. Busbar 4 according toModification 2 has four terminal joints 14. According to busbar 4 havingthree or more terminal joints 14, a battery block in which a pluralityof batteries 2 are connected in parallel can be formed, and the batteryblocks, or the battery block and battery 2, can be connected in series.

Note that a number of terminal joints 14 provided in busbar 4 can beeasily changed by, for example, the following method. That is, flatstranded wire 24 having a length corresponding to the plurality ofbusbars 4 is set on a press working line, and a plurality of terminaljoints 14 are formed continuously or simultaneously in flat strandedwire 24. Thereafter, according to the number of terminal joints 14provided in busbar 4 to be produced, the cutting position of processedflat stranded wire 24 is adjusted. This can facilitate themass-production of busbar 4 having any number of terminal joints 14. Itis thereby possible to enhance the degree of freedom in designingbattery module 1.

(Other Modifications)

In the exemplary embodiment and modifications, terminal joint 14 andvoltage detection line connector 18 are formed in the two stages, whichare the pressure-welding by first press die 34 and the pressure-weldingby second press die 38. However, the present invention is not limited tothis configuration. For example, by using a press die having a steppedpart that corresponds to the difference between the thickness ofterminal joint 14 and the thickness of voltage detection line connector18, terminal joint 14 and voltage detection line connector 18 may beformed simultaneously by one press.

Voltage detection line connector 18 may be omitted. In this case, busbar4, in which coupler 16 and terminal joint 14 are directly connected, isobtained. A number of batteries 2 provided in battery module 1 is notparticularly limited. The structure of each part of battery module 1,including the shapes of end-plate 6 and restraint member 8 and thefastening structures of end-plate 6 and restraint member 8, is notparticularly limited, either.

REFERENCE MARKS IN THE DRAWINGS

1: battery module

2: battery

4: busbar

12: output terminal

14: terminal joint

16: coupler

18: voltage detection line connector

22: slope

24: flat stranded wire

28: precursor terminal joint

30: first region

32: second region

1. A method for producing a busbar that electrically connects aplurality of batteries, the method comprising forming a plurality ofterminal joints that are joined to output terminals of the respectivebatteries by applying pressure to pressure-weld a plurality of electricwires in a plurality of first regions in a bundle of the plurality ofelectric wires, the first regions being arranged at a predeterminedinterval in an extending direction of the bundle.
 2. The method forproducing a busbar according to claim 1, wherein the bundle is a flatstranded wire.
 3. The method for producing a busbar according to claim1, wherein the forming the terminal joints includes forming a slope atan edge close to a non-pressure-welded region in each of the firstregions, the slope having a thickness gradually increasing toward thenon-pressure-welded region.
 4. The method for producing a busbaraccording to claim 1, the method further comprising, before forming theterminal joints, forming a precursor terminal joint in each of the firstregions, and forming a voltage detection line connector in a region ofeach of the second regions except for the corresponding one of the firstregions by applying pressure to pressure-weld a plurality of electricwires in a plurality of second regions each including a correspondingone of the first regions in the bundle.
 5. A busbar electricallyconnecting a plurality of batteries, the busbar comprising: a pluralityof terminal joints that are joined to output terminals of the respectivebatteries; and a coupler that connects the plurality of terminal joints,wherein the coupler is formed of a non-pressure-welded part in a bundleof a plurality of electric wires, and each of the plurality of terminaljoints is formed of a pressure-welded part in the bundle.
 6. The busbaraccording to claim 5, wherein the bundle is a flat stranded wire.
 7. Thebusbar according to claim 5 or claim 6, wherein each of the terminaljoints has a slope at an edge close to the coupler, the slope having athickness gradually increasing toward the coupler.
 8. The busbaraccording to claim 5, comprising a voltage detection line connectordisposed between each of the terminal joint and the coupler.
 9. Thebusbar according to claim 5, comprising three or more terminal joints.10. A battery module comprising: the busbar according to claim 5; andthe plurality of batteries electrically connected by the busbar.